DIPTERA. 75 



the uncovered part. The sucker of blood secretes in a gland placed 

 at the base of his trunk so subtle a poison, that three or four flies 

 are sufficient to kill an ox. 



The Glossina morsitans abounds on the banks of the African 

 river, the Zambesi, frequenting the bushes and reeds that border it. 

 It likes, indeed, all aquatic situations. The African cattle recognise 

 at great distances the buzzing of this sanguinary enemy, and this 

 fatal sound causes them to feel the greatest fear. 



Livingstone, the celebrated traveller, in crossing those regions of 

 Africa that are watered by the Zambesi, lost forty-three magnificent 

 oxen by the bites of the Tsetse fly, notwithstanding that they were 

 carefully watched, and had been very little bitten. 



" A most remarkable feature in the bite of the Tsetse is its perfect 

 harmlessness in man and wild animals, and even calves so long as 

 they continue to suck the cows. We never experienced the slightest 

 injury from them ourselves personally, although we lived two months 

 in their habitat, which was in this case as sharply denned as in many 

 others, for the south bank of the Chobe was infested by them, and 

 the northern bank, where our cattle were placed, only fifty yards 

 distant, contained not a single specimen. This was the more 

 remarkable, as we often saw natives carrying over raw meat to the 

 opposite bank with many Tsetses settled on it. 



"The poison does not seem to be injected by a sting, or by ova 

 placed beneath the skin, for, when one is allowed to feed freely on 

 the hand, it is seen to insert the middle prong of three portions, into 

 which the proboscis divides, somewhat deeply, into the true skin. It 

 then draws it out a little way, and it assumes a crimson colour, 

 as the mandibles come into brisk operation. The previously- 

 shrunken belly swells out, and, if left undisturbed, the fly quietly 

 departs when it is full. A slight itching irritation follows, but not 

 more than in the bite of the mosquito. In the ox this same bite 

 produces no more immediate effects than in man. It does not 

 startle him, as the gad-fly does ; but a few days afterwards the 

 following symptoms supervene : the eyes and. nose begin to run, 

 the coat stares as if the animal were cold, a swelling appears under 

 the jaw, and sometimes on the navel ; and, though the animal 

 continues to graze, emaciation commences, accompanied with a 

 peculiar flaccidity of the muscles, and this proceeds unchecked until, 

 perhaps months afterwards, purging comes on, and the animal, no 

 longer able to graze, perishes in the state of extreme exhaustion. 

 Those which are in good condition often perish, soon after the bite 

 is inflicted, with staggering and blindness, as if the brain were 



